PROJECT SUMMARY ApoE is the strongest risk factor for Alzheimer's Disease (AD). It is known that the risk conveyed by the ApoE e4 allele is strongest in Asians>Non-Hispanic Whites (NHW) > African-Americans (AA). It was not known if this ?protective effect? for AA was due to a difference between these ethnic groups in ApoE and/or its surrounding genomic region, or a function of some ethnic difference in other genomic regions, interacting with ApoE, reducing risk. However, we have recently performed admixture studies on Puerto Rican AD (PRADI) cases and controls, and find that PRADI participants who inherited an approximately 2 mB African admixture block region containing ApoE have a lower risk of AD as well, similar to that described for AA, independent of their overall genomic admixture. PRADI cases that inherited the NHW ApoE admixture block have the same elevated ApoE e4 risk as NHW. This highly suggests the ?protective? effect is due a genetic change in this 2mB African admixture block surrounding the ApoE region. Preliminary data examining sequence differences between the African e4 allele, NHW e4 allele and Japanese e4 allele, pulled from the 1000 genomes database, demonstrates a very strong, shared peak of sequence differences between the NHW and Japanese versus the African block, lying within one of the strongest topological associated domain regions (TAD) for ApoE in the hippocampus. This supports the hypothesis that a variant or variants in the region are involved in reducing ApoE e4 risk. All of significant variants are non-coding, and thus likely to represent regulatory effects. This proposal will determine transcriptome and cellular differences between the two different e4 admixture blocks, using multiple approaches. Successful outcome of this work would identify the protective variant for ApoE e4 lying in the African region and could lead to new intervential therapy to reduce the risk of ApoE e4 for AD. Specifically we propose to: 1) refine the significantly different variants between the admixture blocks 2) identify variants based on function and location 3) evaluate genomic and cellular differences between APOE e4/4 admixture blocks; and 4) conduct cross-culture experiments and isolate the actual variants using CRISPR/CAS9 genomic editing.